Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16B—DEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
  • F16B19/00—Bolts without screw-thread; Pins, including deformable elements; Rivets
  • F16B19/04—Rivets; Spigots or the like fastened by riveting
  • F16B19/08—Hollow rivets; Multi-part rivets
  • F16B19/10—Hollow rivets; Multi-part rivets fastened by expanding mechanically
  • F16B19/1027—Multi-part rivets
  • F16B19/1036—Blind rivets
  • F16B19/1045—Blind rivets fastened by a pull - mandrel or the like
  • F16B19/1054—Blind rivets fastened by a pull - mandrel or the like the pull-mandrel or the like being frangible

Definitions

• the present invention relates to the field of blind fasteners, and sore particularly to blind fasteners of high strength and high fatigue life as ara used in aircraft manufacture and the like.
• the present invention comprises an improvement to the Blind Rivet Assembly With Locking Collar And Rivet Stem disclosed in U. S. Patent No. 4,012,984. That patent discloses a blind rivet assembly having a blind rivet stem extending through a hollow rivet so that it may be pulled, thereby to expand the tail of the hollow rivet.
• a collar on the stem has a head fitting in a locking groove within the grip length of the stem so that when the tail of the collar abuts a pressure element bearing against the head of the hollow rivet, it is bulged outwardly into a recess in the rivet head, thereby to interlock the rivet stem in the hollow rivet.
• a weakened portion, such as a break groove, is provided on the stem adjacent the bulged end of the collar whereby upon further pulling, the rivet stem breaks at the weakened portion, leaving the remaining part of the blind rivet assembly in the workpiece.
• Such a blind rivet assembly has found substantial uses in aircraft construction and other applications.
• the design and operation of the locking collar of such blind rivets have certain characteristics which may result in loose stems upon installation or after some period of use, and which may result in the installed fastener exhibiting less than its full strength and fatigue life potential.
• the locking collar must fit within the locking groove and rivet sleeve for all combinations of tolerances of parts, with the worst combination being the largest allowable locking, groove and the smallest allowable locking collar. Consequently, the locking collar will fit slightly loosely within the locking groove for all other combinations of dimensions, even when the parts are right on the nominal dimensions.
• the locking collar is forced toward the tail of the rivet sleeve, to the extent it has clearance with respect to the locking groove, so that the stem of the installed rivet may move slightly toward the rivet tail under conditions of high stress or vibration, thereby reducing the strength and fatigue resistance of the rivet.
• the skirt of the locking collar is effectively formed on installation by the buckling of the upper skirt portion of the locking collar, the folding or buckling action of the skirt necessitates a rather deep recess in the sleeve head. This results in an overlap between this recess and the locking groove of the mandrel.
• a locking apparatus for blind fasteners providing improved yield and fatigue performance of the blind fasteners utilizes a locking collar which will slide over the fastener stem and within the tubular rivet, sleeve of the fastener without preforming into the locking groove on the stem.
• the locking collar is formed so that upon the pulling of the stem during installation of the blind fastener, specially formed tapered reliefs in the locking collar then adjacent the locking groove on the stem cause.the region of the locking collar immediately thereabove to be forced tightly inward against the locking groove to provide a particularly tight fit in the locking groove.
• a specially tapered top end of the locking collar is flared outward into the recess in the fastener head, and the tubular shank is expanded in compression to take up any clearances thereabout, all of the foregoing occurring before the breaking of the pulling portion of the stem occurs.
• the net result is that the flared portion of the locking collar fits tightly in the recess, the other end of the locking collar fits tightly in the locking groove and the cylindrical portion therebetween fits tightly on the adjacent portion of the stem and tightly within the adjacent portion of the rivet sleeve, independent of reasonable variations in the dimensions of the various components of the blind fastener within the dimensional tolerances of such components.
• Alternate forms of the top end of the locking collar and in the recess in the fastener head particularly suited for use in fasteners wherein fastener head material will be removed after installation for surface smoothing purposes are disclosed.
• Figure 1 is a cross section, partially cut away, of the rivet of the present invention as inserted but prior to pulling
• Figure 2 is a view similar to Figure 1 after pulling and immediately prior to the breaking of the pulling portion of the stem from the stem in the installed rivet
• Figure 3 is a partial cross section taken on an expanded scale illustrating the breaking away of the pulling portion of the rivet stem
• Figure 4 is & side view taken in partial cross section of the locking collar of the present invention
• Figure 5 is a partial cross section of the rivet of the present invention illustrating on the left side of the center line the rivet prior to pulling and the right side of the center line the rivet after pulling
• Figure 6 is view taken on an expanded scale along line 6-6 of Figure 5
• Figures 7 through 9 and 11 are views illustrating various characteristics of a prior art locking collar
• Figure 10 is a view illustrating the flaring of the top of the locking collar of the present invention during pulling.
• Figure 12 is a schematic cross section of the top of the locking collar of the embodiment of Figures 1 through 11 before and after pulling, taken on an expanded scale.
• Figure 13 is a schematic cross section of the top of an alternate embodiment locking collar before and after pulling.
• Figure 14 is a schematic cross section of the top of a still further alternate embodiment locking collar before and after pulling.
• a blind rivet assembly inserted in an appropriate hole through two plates to be joined prior to pulling and during pulling, respectively, may be seen.
• the major parts of the rivet for purposes of identification, comprise the tubular rivet sleeve 10 having an expandable sleeve tail 12 and preformed head 14, with a stem, generally indicated by the numeral 16, passing therethrough.
• the stem has a pulling portion 18, a plug portion 20 basically conforming to the inner diameter of the rivet sleeve 10, a smaller diameter portion 22 thereabove, a locking groove 24 between the plug portion 20 and the smaller diameter region 22, and a tail former 26 at the lower end thereof.
• These various parts of the blind rivet assembly in the present invention are generally in accordance with the corresponding parts of U.S. Patent No.
• the present invention includes a locking collar 28 of particularly unique design, which in cooperation with the various other elements of the blind rivet assembly, provides an improved locking action for the stem of the installed rivet, helping to eliminate the occurrence of any looseness in the installed rivet and improving the stress and fatigue capabilities of the rivet.
• a pressure washer 30 is used which, as shall be subsequently seen, acts as an anvil during pulling, against which the head of the locking collar is formed. Other embodiments do not use the pressure washer, the same function being achieved by the abutting face of the pulling tool.
• FIG 2 illustrates the rivet of Figure 1 during pulling.
• the pulling tool generally comprises a pressure element 32 through which the pulling portion 13 of the stem will pass so that the pressure element may rest flat against the pressure washer 30.
• the pulling tool also has a chuck-like portion, generally indicated by the numeral 34, which engages the pulling portion 13 of the stem, and through a mechanism not shown will pull the pulling portion of the stem along its axis until the sleeve tail 12 is expanded by the tail former 26 and the locking collar 28 is formed to lock the stem at the pulled position, after which the pulling portion 18 of the stem will break frpm the lower portion of the stem as shown in Figure 3 by the failure of the stem in tension at the break groove 36 (see Figure 1) in the stem provided to define a weakened region therein.
• the locking collar 23 of the present invention may be seen in Figure 4, which is a side view, partially cut away to also illustrate a cross section thereof.
• the locking collar of the preferred embodiment is a generally tubular member specially formed in three regions.
• adjacent the lower end thereof is internal taper 33 just above a short tubular section 40.
• Cooperatively disposed with the internal tapered region 38 is an external tapered region 42, the upper portion 43 and the lower portion 50 of the locking collar being connected between the two tapered regions by section 44.
• the top of the locking collar 23 has an internal tapered region 46 extending outward at the top of the locking collar to at least a substantial part of the wall thickness of the basic tubular shape of the locking collar.
• FIG. 5 an illustration showing at one side of the center line the various parts of the blind rivet before pulling, and on the other side of the center line the rivet after pulling, may be seen.
• the locking collar 23 may be located anywhere along the rivet stem between the plug portion 20 and the pressure washer 30, as unlike the prior art, the locking collar is not preformed onto the stem and more particularly into the locking groove in any way. Thus, obviously though assembly of the various parts is required, a preforming step onto the stem is not.
• the locking collar 23 after pulling may be seen in the right hand portion of Figure 5, with the relevant portion of such figure being shown on an expanded scale in Figure 6.
• Figure 6 it may be seen that the lower portion 50 has been forced downward firmly against the sleeve head 14 so as t ⁇ eliminate any clearance therebetween.
• the region 44 joining the lower portion 50 and the upper portion 43 of the locking collar ( Figure 4) has been greatly distorted, and in fact may partially or totally fracture without consequence.
• the tapered upper region of the lower portion 50 of the locking collar has in effect formed an inclined plane, cooperating with the outer tapered region 42 of the locking collar 23 to force the lower region 52 of the locking collar to deform inward to substantially totally fill the locking groove in the rivet stem, independent of the exact dimensions of the various parts within the allowed range of tolerances.
• the locking collar wedges tightly against the upper region of the locking groove, thereby avoiding any clearance therebetween in the set rivet.
• the locking collar of the present invention does not have any regions of enlarged cross section such as the head 56 of Figures 7 through 9, but in fact because of the tapered regions 42 and 38, the regions of the locking collar which are formed into the locking groove are in effect the same or lesser thickness than the tubular region 63 of the locking collar. Accordingly, the portions of the locking collar forming in the regions of the locking groove readily deform and yield in compression t ⁇ assure very tight filling of the locking groove, independent of the particular dimensions of the various parts within the allowed tolerance range.
• Figure 6 is a drawing accurately illustrating on an expanded scale, the cross section of the locking collar and adjacent regions of the rivet after pulling.
• top of the locking collar 23 flares outward as a result of the tapered region 46 ( Figure 4) of the locking collar.
• the pressure washer 30 engages the top of the taper, which top is at or toward the outside diameter of the cylindrical region 68 of the locking collar.
• the compressive stresses adjacent the top of the locking collar during formation are highest adjacent the outside diameter of the locking collar, inducing compressive yielding in that region first to result in the flaring of the top of the locking collar as illustrated in Figure 10 to form the flared top 70 of the locking collar to lock the locking collar in the recess 72 of the preformed head 14 of the rivet.
• the top 74 of the locking collar is forced to buckle t ⁇ serve the same function, thereby requiring a bigger and particularly a deeper recess in the head of the rivet, which frequently results in an overlap between that recess and the locking groove of the mandrel.
• Such an overlap is undesirable, the occurrence of such buckling outward tending to roll the top of the head of the locking collar out of the locking groove in the stem, further increasing any clearance in that region.
• the tubular portion 68 (Fig. 6) of the locking collar yields in compression to fully fill any clearance between the smaller diameter portion 22 of the stem and the adjacent inside diameter of the rivet sleeve head 14.
• the rivet sleeve must be somewhat malleable for the sleeve to be somewhat expanded to fill the hole in the parts to be joined and for the tail of the sleeve to be properly expanded by the tail former. Consequently it is particularly important that the entire inner diameter of the rivet sleeve be supported internally by tight fitting parts and/or parts compressively distorted thereinto, as any clearance between the rivet sleeve and the stem would allow the rivet sleeve to distort in use under load, reducing the strength and fatigue life of the assembly. It is of course also important that the stem of the installed rivet be as positively locked in the set position as.
• the stem may allow the stem to move in the direction of the tail of the rivet upon the shock of the breaking of the stem, or subsequently in use of the rivet, reducing the support for and thus the strength of the sleeve and tail of the installed rivet.
• the present invention locking collar provides optimum filling of the locking groove in the stem, independent of part dimensions, assures uniform compressive deformation of the locking collar in the tubular portion thereof to assure tight filling of the respective region between the stem and the sleeve (and to help expand the sleeve ⁇ and provides a definite and positive flaring of the top of the locking collar into a recess in the head, of the sleeve of minimum size, all to provide a blind rivet assembly of the highest strength and fatigue resistance.
• the lower portion 50 of the locking collar could be formed as the upper portion of the plug portion 22 of the stem, though again such is not preferred as to do so would in effect require the formation of a locking groove generally conforming to the lower part 52 of the installed collar (see Figure 6), a difficult locking groove t ⁇ both fabricate and inspect.
• taper 46 at the top of the locking collar -of Figure 4 is shown as encompassing most of the diameter of the locking collar so as to define a relatively thin section ring at the top of the locking collar, the extent of this taper can be varied as desired in relation to the various other dimensions and proportions of the various parts making up the rivet, as the flaring will generally occur providing the taper is of at least some substantial extent, and preferably is of at least 50% of the thickness of the cylindrical section 63.
• the diameter of the bottom of the tapered region 42 be smaller than the diameter at the top of tapered region 33 so that the tapered regions themselves will engage as inclined planes upon distortion of section 44, such is not an absolute requirement, as the desired action will occur so long as these two diameters are at least approximately equal.
• Figure 12 is an enlarged view of the top of the locking collar and the recess in the head of the fastener, the left side of the figure illustrating the part3 before pulling and the right side illustrating the parts after pulling.
• the tapered region 46 encourages the flaring of the top of the locking collar, with a very good tight filling of the recess 72 in the head of the rivet as a result thereof.
• the second condition which is sometimes encountered is a result of the shaving of the head of installed fasteners, sometimes done to provide an especially smooth aerodynamic surface across the top of the installed fasteners, and to assure that the surface of the installed fastener is flush with the surface of the adjacent material.
• the head may be shaved to a level approximately equal to the level indicated by the dashed line 32 in Figure 12. It may be seen therein that this extent of shaving will remove a substantial portion of the flare, leaving such a small portion of the flare as to appear to substantially weaken the effective retention of the stem by the locking collar.
• unshaved fasteners in accordance with the present invention are substantially stronger in this respect than prior art fasteners, and that while the shaving does slightly reduce the strength of the fastener, the strength of the shaved fastener still equals or exceeds that of the prior art devices.
• the strength of the shaved fastener still equals or exceeds that of the prior art devices.
• the cylindrical recess 34 is approximately the same depth or perhaps even shallower than the depth of the cylindrical recess portion of recess 72 of the earlier design.
• the cylindrical recess 84 is of generally smaller diameter than the diameter of the cylindrical portion of recess 72 of the earlier design, though the tapered region 86 is a much deeper taper than before.
• the top of the locking collar 23 is generally symmetrically rounded so that the pressure thereon during forming of the head is essentially distributed over a ring or annulus substantially midway between the inner and outer diameter thereof. This in turn discourages flaring of the top of the locking collar but instead induces compressive yielding or upsetting of the locking collar on pulling, as in illustrated in the right hand portion of Figure 13.
• the relief 86 adjacent the inner diameter of the locking collar prior to pulling formed by the radius on the top of the locking collar shown in Figure 13, a chamfer or otherwise, allows for substantial material flow in that region without extruding outward between the stem and the anvil washer, resulting in the substantial filling of the relieved area upon pulling, as shown as 33 in Figure 13, without any extrusion of material into the region between the inner diameter of the anvil washer and the stem.
• the embodiment of Figure 13 achieves the desired result of eliminating the extrusion of any locking collar material between the anvil washer and the stem, and assures sufficient depth in the formed top of the locking collar after pulling so as to eliminate any appearance of significant weakening of the lock after shaving.
• the relatively long tapered region 36 together with the fact that the forming force on the top of the locking collar during pulling is approximately centered on the cross section thereof, may result in an und ⁇ sirsd buckling or bulging of the locking collar away from the stem in the region of the fastener head recass, as indicated by the dashed line 92 of Figure 13.
• This of course is also undesirable, and accordingly, there is a definite limit on the depth of the tapered region 36 which may be used without encountering this problem.
• the recess in the head of the fastener and associated region of the locking collar may be seen in Figure 14.
• the recess 94 in the head of the fastener is substantially deeper than the recess 72 ( Figure 12) of the first disclosed embodiment, and is also of a substantially smaller diameter.
• the tapered region 96 at the bottom of the recess 94 is a somewhat deeper taper than the corresponding region 98 of the embodiment of Figure 12, but not as deep as the embodiment of Figure 13.
• the depth of the recess 72 in the embodiment of Figure 12 is approximately equal to the annular thickness of the locking collar 23 so that a simple flaring of the locking collar will substantially fill the recess.
• buckling is avoided by the fact that the unsupported length of the locking collar within the recess in comparison to its thickness is still relatively short, and the partial flare of the top of the locking collar outward to engage the wall of the recess leaves both the inner diameter and outer diameter of the unsupported length of the locking collar unconstrained, whereby the locking collar will yield in compression to fill the recess as shown before buckling can occur.

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• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Insertion Pins And Rivets (AREA)

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• 1985
  • 1985-09-04 EP EP19850904704 patent/EP0192758A4/fr not_active Withdrawn
  • 1985-09-04 WO PCT/US1985/001686 patent/WO1986001565A1/fr not_active Application Discontinuation

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